Welcome to John’s Blog. Answers to frequently asked questions are periodically posted here. The objective is to share information about PVC pipe with readers as well as with utilities, design engineers and pipe installers. The blog will provide the latest information on PVC pipe design, installation, and application for water and wastewater infrastructure projects.

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John Houle: Technical Director

John Houle is Uni-Bell’s Technical Director. John holds a Master’s Degree in Civil Engineering from the University of Missouri and an MBA from the University of Oregon. He has more than 25 years of experience in the plastic pipe industry in applications engineering, market development, forensic analysis, technical writing, and standards development.

John Houle,
Technical Director

Transitioning Between Ductile Iron and PVC Pipes

Posted on December 10, 2014 by John Houle

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When it is necessary to transition between PVC and DI pipe, there are several considerations to keep in mind.

First, although both products are made to the same Cast-Iron outside diameter (CIOD) regimen, ductile iron pipe tolerances are much looser than those for PVC pipe. This has an effect on some joining situations.

Second, the geometry of the two products’ spigot ends is very different. This means that inserting PVC bells into DI spigots is easily accomplished, while inserting DI spigots into PVC bells is more problematic.

It is estimated that there are more than a million miles of installed PVC water pipe in rural communities across America – enough to go to the moon and back twice. At an average of say $20 per foot installed, that’s more than $100 billion in pipe value!

The majority of this pipe was manufactured to ASTM D2241, which is celebrating its 50th anniversary this year.

ASTM D2241 pipe has also been installed in many municipal water and forcemain systems. Prior to the introduction of AWWA C900 in 1975, D2241 pipe was the product of choice for PVC pressure pipe systems, so it is not just a rural product.

ASTM D2241 has played a significant role in U.S. piping infrastructure by providing the requirements for materials, dimensions, and product testing that has ensured users a high-quality pipe product.

On its website the Plastics Pipe Institute (PPI) has a design tool called “PACE” (Pipeline Analysis and Calculation Environment), for the design of surge pressures for plastic pipes. The tool includes comparison of PE and PVC pipes.

However, it is important to realize that although the word “Plastics” appears in its name, PPI does not speak for PVC. In fact, PPI has misrepresented PVC in favor of PE.

PACE is an example.

While the tool itself is functional, restrictions placed on the input variables force the results to be skewed in favor of PE. I tried to use PACE to verify the design example in the AWWA C900 standard for PVC pipe, but could not because PACE will not allow the use of the standard’s inputs!

By contrast, PE has less rigorous justification for its cyclic-surge design methodology. AWWA Standard C906 for polyethylene pipe contains only design values without any technical explanations.

The Bottom Line

Driven by PPI’s interest to develop design tools that favor PE, PPI has intentionally mandated that only highly unlikely design assumptions and inputs be used for PACE when it comes to PVC pipe. The flawed results produced for PVC pressure pipe are not consistent with its performance in the field over many decades or studies confirming PVC pipe longevity at more than 100 years.

Time to Redefine “Large Diameter” PVC Pressure Pipe

Posted on September 30, 2014 by John Houle

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In 1975 AWWA published the C900 standard for PVC pressure pipe and fittings. The standard’s product sizes ranged from 4-inch through 12-inch. In 1988 a second PVC pressure pipe standard was published – this standard, AWWA C905, included sizes from 14- through 24-inch.

The two standards differed markedly in their product design: C900 used a safety factor of 2.5, while C905 employed an SF of 2.0. Because of this distinctly different design approach, there was an obvious break between small diameter pipe (4- through 12-inch) and large-diameter pipe (14- through 24-inch.)

In the 26 years since C905 was published, however, three major changes have occurred that make the transition point to large diameter less clear:

The design methods in the two standards have been harmonized.

A revision is now under way at AWWA to merge the two standards under the C900 title.

The largest size being produced has more than doubled to 60 inches.

What was considered “large-diameter” in 1988 is now relatively small. Unfortunately, some specifiers still consider 14-inch as a large pressure pipe – with 60-inch as the comparison, I think it is time to revisit the definition of “large-diameter.”

PVC’s market share for potable water mains and sewer forcemains in North America has been growing steadily for more than 50 years. The large market share gained by smaller-diameter PVC pipe is a result of the product’s outstanding performance characteristics – the same advantages that are provided by larger-diameter products.

Time to Update Specifications for ASTM F679 PVC Sewer Pipe

Posted on September 23, 2014 by John Houle

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In 1980 ASTM published its F679 standard for solid-wall PVC pipe and fittings. The standard’s design philosophy was to allow two wall thickness options (called “T1” and “T2”) based on two values for the PVC material’s modulus of elasticity.

In 2006 this design method was changed. Gone are the “T1” and “T2” wall designations.

Instead the new system provides a minimum wall thickness table combined with minimum pipe stiffness values – the pipe manufacturer is now able to provide the targeted pipe stiffness with any combination of wall thickness and modulus of elasticity (as long as material cell class and minimum wall thickness requirements are met).

The bottom line: project specifications that call out “T1” or “T2” walls are outdated – these references have been obsolete for about eight years.

Time to Redefine “Large Diameter” Solid-Wall PVC Gravity Sewer Pipe

Posted on September 17, 2014 by John Houle

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In 1980 ASTM published its F679 standard for solid-wall PVC pipe and fittings. The standard’s title, “Polyvinyl Chloride (PVC) Large-Diameter Plastic Gravity Sewer Pipe and Fittings,” was appropriate at the time, because the product sizes ranged from 18-inch to a maximum size of 27-inch.

In the thirty-four years since 1980, however, the maximum size more than doubled to 60 inches. What was considered “large” in 1980 is now relatively small.

Unfortunately, some specifiers still consider 18-inch as a large sewer pipe – with 60-inch as the comparison, I think it is time to revisit the definition of “large-diameter.”

PVC sewer pipe has been the product of choice for sanitary sewers in North America for more than 25 years. The large market share gained by smaller-diameter PVC pipe is a result of the product’s outstanding performance characteristics – the same advantages that are provided by larger-diameter products.

Pipe Stiffness Explained: PVC and Ductile Iron

Posted on June 11, 2014 by John Houle

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Some project specs require Ductile Iron (DI) pipe because of its supposed “strength” in resisting external loads. In the past it was true that iron pipe had plenty of pipe stiffness, but that was before the iron industry converted from thicker-walled Class pipe to thinner-walled Pressure Class pipe.

Conventional Wisdom Is Not Always True

This tech brief discusses how much a pipe can safely deflect – PVC is safer.

Pipe stiffness of two approximately equal pressure class pipes is compared – PVC is stiffer.

The facts:

DI pipe fails at a lower deflection than PVC pipe.

DI has a lower safety factor against failure.

Conventional wisdom is turned on its head: the stronger, safer pipe is PVC!

Looking Back 20 Years at AWWARF’s 1994 Study on PVC Water Pipe Performance

Posted on May 14, 2014 by John Houle

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In 1994 AWWA’s Research Foundation published a report on PVC pipe titled “Evaluation of Polyvinyl Chloride (PVC) Pipe Performance.” We have now reached the 20th anniversary of the study – time for a look back to see if the research findings were accurate.

I’ve tried to keep you in suspense, but the answer is a resounding “Yes.” The report’s assertions have proven correct and time has reinforced its conclusions. For example:

The allegation that PVC “loses strength with time” has been disproved.

Tapping PVC pipe was not a problem back then and is less so today with improvements in hardware, procedures, and tapping.

UV exposure and chemical permeation of PVC pipe were shown by AWWARF to be non-issues 20 years ago and the passage of time has borne this out.

PVC water pipe was in widespread use in North America 20 years ago, but has now become the product of choice – it is a well-engineered product that provides exceptional service for water transmission and distribution systems.

PVC Pipe Materials: Cell-Class Explained

Posted on April 29, 2014 by John Houle

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Product standards for PVC water and sewer pipes typically require PVC materials to meet ASTM cell-class requirements. The cell class consists of five cells that designate different aspects of the material.

This tech brief discusses cell class and what all those numbers mean. It also takes issue with two industry misconceptions:

The 12364 cell class is “new” – the truth is that this class has been in ASTM standards for about 35 years – this is not new!

PVC cell class is 5 numbers plus one letter – this was correct in the past, but ASTM eliminated the letter more than 15 years ago – this is not new either!